1. Field of the Invention
The present invention relates to a zoom lens system which includes a standard focal-length range to a intermediate telephoto range.
2. Description of Related Art
Zoom lens systems which includes a standard focal-length range to a intermediate telephoto range and which is configured of four lens groups, i.e., a configuration of a positive lens group, a negative lens group, a positive lens group and a positive lens group, in that order from the object side, or a configuration of a negative lens group, a positive lens group, a negative lens group and a positive lens group, in that order from the object side, are known in the art.
In the zoom lens system configuration of a positive lens group, a negative lens group, a positive lens group and a positive lens group, in that order from the object side, it is predominant for such a zoom lens system to have a function for correcting hand-shake (image-stabilizing function) by decentering a predetermined lens group (image-stabilizing lens group). In such a zoom lens system configuration, although there are advantages of being able to miniaturize the image-stabilizing lens group and being able to increase the zoom ratio, there is a disadvantage of deterioration in optical performance occurring during manufacture due to the error sensitivity thereof being high.
Whereas, in the zoom lens system configuration of a negative lens group, a positive lens group, a negative lens group and a positive lens group, in that order from the object side, although there is the advantage of the optical performance, at the design stage, not easily deteriorating during manufacture due to the error sensitivity being low, there is the disadvantage of it being difficult to improve the optical performance at the design stage if the zoom lens system is further miniaturized (and reduced in weight) in order to achieve a high zoom-ratio and/or provide an image-stabilizing function. Accordingly, there are very few zoom lens systems which employ a configuration of a negative lens group, a positive lens group, a negative lens group and a positive lens group, in that order from the object side, while providing an image-stabilizing function.
Japanese Unexamined Patent Publication Nos. 2010-217535 and 2009-14761 both disclose a zoom lens system having a negative lens group, a positive lens group, a negative lens group and a positive lens group, in that order from the object side, which is provided with an image-stabilizing function and in which the third lens group, which has the smallest diameter out of all four lens groups, is utilized as an image-stabilizing lens group. The third lens group that constitutes as an image-stabilizing lens group includes a cemented lens that is provided with a positive lens element and a negative lens element.
However, in the zoom lens system of each of the above-mentioned Japanese Unexamined Patent Publication Nos. 2010-217535 and 2009-14761, since the negative refractive power of the first lens group is too strong compared to the positive refractive power of the second lens group (since the balance of refractive power between the first lens group and the second lens group is inappropriate), resulting in the diameter of the light bundle that is incident on the lens groups that are provided rearwardly from the first lens group (i.e., the second lens group, the third lens group and the fourth lens group) becoming too large, a large amount of coma occurs, thereby deteriorating the optical quality. Furthermore, since the refractive power of the bonding surface between the positive lens element and the negative lens element of the cemented lens that is provided within the third lens group (the image-stabilizing lens group) is inappropriate, high-order aberrations that occur in the third lens group cannot be sufficiently cancelled out, so that the change in optical performance during an image-stabilizing operation increases, thereby deteriorating the optical performance.
Japanese Unexamined Patent Publication No. 2008-216881 discloses a zoom lens system which is not provided with an image-stabilizing function and is configured of a negative lens group, a positive lens group, a negative lens group and a positive lens group, in that order from the object side; however, even if this zoom lens system were to use the third lens group thereof as an image-stabilizing lens group, and the same problems as those in the zoom lens systems of the above-mentioned Japanese Unexamined Patent Publication Nos. 2010-217535 and 2009-14761 would occur.